Printer or copier with an arrangement for printing both sides of a recording medium

ABSTRACT

A printer or copier operating according to the transfer printing principle containing an arrangement for printing the front and/or the back of a recording medium. The apparatus contains a photoconductor drum and a thermoadhesive transfer ribbon which is coupled to the photoconductor drum. The transfer ribbon proceeds to a transfer printing and fusing station formed by the transfer ribbon on one side and a heated roller on an opposite side in elastic contact thereto. A first toner image for the back of the recording medium and a second toner image for the front of the recording medium are produced on a photoconductor drum and transferred to the transfer ribbon in this order. The heated roller first receives a toner image for the back of the recording medium. Thereafter, the recording medium is fed to the fusing gap and simultaneous transmission and fusing of the toner image on both sides of the recording medium takes place by the transfer ribbon and the heated roller moving across both sides of the recording medium.

BACKGROUND OF THE INVENTION

The invention relates to an arrangement for printing the front or theback of a recording medium in a printer or copier which operatesaccording to the transfer printing principle and to a method foroperating an arrangement of this kind.

Printers or copiers for simplex or duplex printing are disclosed forexample in U.S. Pat. No. 4,477,176 and U.S. Pat. No. 4,537,493. Theseare electrophotographic printing devices with a photoconductor on whichat least two charge images can be arranged one behind the other, thesaid printing devices also having a transfer printing station withassociated single-sheet positioning device (turning device) whichpermits the electrophotographic printing device to be operated in twooperating modes, specifically, in a first operating mode in which theinked-in toner images which are arranged one behind the other on thecharge image carrier are arranged one on top of the other or next to oneanother on one side of the single sheet, and in a second operating modein which the sequence of toner images located on the charge imagecarrier are arranged on the front and the back of the single sheet. Thefusing of the toner images on the single sheets is carried out with theaid of a roller fusing station using pressure and high temperatures.

In the duplex printing operating mode in which one toner image isarranged on each side of the single sheet, the fusing of the front andback takes place simultaneously. For this purpose, the single sheetwhich is printed on one side must be turned and printed again on theother side, and it is subsequently conveyed in a contactless fashion tothe roller fusing station, for example by means of an air cushion.

This requires a very high degree of mechanical expenditure if a highdegree of operating reliability is to be ensured over a large range ofprint matter.

It is to be generally noted that any braking, accelerating and turningdevice in the printer or copier exerts forces on the recording mediumwhich make exact positioning of the recording medium, and thus reliableguidance of the recording medium in the copier or printer, moredifficult. This increases the risk of blockages considerably, which canlead to frequent equipment failures. Turning, before fusing, a recordingmedium provided with toner images requires a considerable degree ofexpenditure control in order to prevent the toner images becomingblurred.

Furthermore, U.S. Pat. No. 2,990,278 and GB-A-2,040,226 discloseelectrophotographic printing devices in which character-dependent chargeimages are produced on a photoconductor with the aid of an exposuredevice and are fed to a developer station. The developed charge image isthen mechanically lifted off from the photoconductor using pressure withthe aid of a ribbon-shaped transfer element and transmitted to arecording medium. In order to be able to fuse the toner image on therecording medium, the toner image is heated on the ribbon-shapedtransfer element with the aid of a heating device and the heated tonerimage is applied to the recording medium by means of a rollerarrangement using pressure and heat. After the transfer of the tonerimage onto the recording medium, the ribbon-shaped transfer element iscleaned of adhering toner in a cleaning station.

WO 82/00723 discloses an arrangement and a method for printing arecording medium on both sides. In this process, a charge image isgenerated on a photoconductor and then, with the aid of this chargeimage, an electrostatic charge image is produced on a dielectric rolleror drum by ionography. It is also possible to form the charge imagedirectly on the dielectric roller by means of an ion generator. Afterdevelopment with the aid of a developer station by applying a singlelayer of toner of a single-component developer, the single-layer tonerimage which is associated with the back of the recording medium istransferred, using pressure only and without heat, onto a recordingroller arranged underneath the dielectric roller. Afterwards, in thesame way, a toner image which is associated with the front of therecording medium is formed on the dielectric roller and then, againusing pressure only and without heat the two toner images aresimultaneously transferred to the front and back of the recordingmedium.

SUMMARY OF THE INVENTION

The object of the invention is to provide an arrangement for printingthe front and/or the back of a recording medium in a printer or copieroperating according to the transfer printing principle, and a method foroperating an arrangement of this kind which permits simultaneousprinting and fusing of the recording medium on the front and the back inonly one operational procedure.

A further object of the invention is to achieve, with a minimum degreeof expenditure on control, optimum accuracy of fit of the print imageson the recording medium.

The object of the invention is achieved by an arrangement forsingle-color or multi-color printing the front and back of a recordingmedium in a printer or copier operating according to the transferprinting principle having an electrophotographic device with aphotoconductor for producing a sequence of toner images on thephotoconductor. A transfer printing and fusing station is providedhaving a transfer printing and fusing gap assigned thereto fortransferring toner images to a recording medium such as a piece ofpaper.

A transfer ribbon having associated electrostatic transfer meansreceives toner images from the photoconductor and conveys the tonerimages to the transfer printing and fusing station. One or more heatingdevices can be used for heating the toner images in such a way that theyare in a pasty, sticky state. The transfer printing and fusing gap,which is assigned to the transfer printing and fusing station, is formedby the transfer ribbon on one side and a transfer printing and fusingelement on an opposite side, arranged in such a way that the transferribbon and the transfer printing and fusing element are supportedelastically on one another.

The transfer printing and fusing element and the transfer ribbon havesurfaces which receive the toner images of such a quality that, oncontact with the transfer ribbon, the transfer printing and fusingelement removes a warm toner image which is arranged on the transferribbon and is in a pasty, sticky state. A recording medium conveyingdevice is provided for feeding the recording medium to the transferprinting and fusing gap such that, as the recording medium passesthrough the gap, the transfer printing and fusing element and thetransfer ribbon roll on the recording medium and, in this process, thewarm toner images are transferred to the recording medium.

Advantageously, the transfer printing and fusing element is constructedas a heated roller or a heated ribbon. The transfer printing and fusingelement has a circumferential length which is determined in accordancewith a strictly prescribed consecutive spacing of image areas whichreceive the tone images on the photoconductor. A cleaning device can beprovided which is assigned to the transfer printing and fusing elementand can be activated as required. A heating device can be providedassigned to the transfer printing and fusing station and/or to thetransfer ribbon. A preheating device which preheats the recording mediumcan advantageously be used before the recording medium is fed to thefusing gap. The surface layer of the transfer ribbon can comprise asilicon or silicon-like material and a surface layer of the transferprinting and fusing element can comprise a fluoroplastic containingsurface layer.

The invention permits simultaneous print transfer with simultaneousfusing in only one operational procedure. The recording medium can movein a completely straight path through the printer or copier at acontinuous speed. No accelerating and braking processes are necessary toprint and fuse the recording medium. A turning device can be dispensedwith.

By virtue of the rigid, geometrically accurately determined process, ahigh degree of accuracy of fit with a minimum degree of expenditure oncontrol is achieved.

Both upstream and downstream of the transfer printing and fusing stationthere is no print image on the recording medium to become blurred. Thus,it is possible to guide and convey the recording medium on both sidesboth upstream and downstream of the transfer printing and fusingstation.

The single processing procedure for simultaneous transfer printing onboth sides using low-temperature fusing leads to non-wearing processingof the recording medium. As a result, warping and distortions in therecording medium are prevented.

The arrangement permits full-color printing without additionalexpenditure in the transfer printing and fusing station.

In an appropriately selected material combination of the surfaces of thetransfer ribbon which bear the toner images, and of the transferprinting and fusing element it is possible, if desired, to dispense withthe arrangement of an additional cleaning device for these components ofthe printer or copier.

One embodiment of the invention is illustrated in the drawings and isdescribed in greater detail below by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic sectional view of an arrangement forprinting the front and/or the back of a recording medium in a printeroperating according to the transfer printing principle, and

FIG. 2 shows a diagrammatic side view of the transfer printing andfusing station used in the arrangement in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrated electrophotographic single-sheet printing device forsingle-color or multi-color printing of single sheets in simplex mode orduplex mode contains an intermediate carrier 10 in the form of aphotoconductor drum which is driven by electric motor. However, insteadof the photoconductor drum an OPC ribbon can also be arranged. Groupedround the first intermediate carrier 10 are the various assemblies forthe electrophotographic process. These are essentially: a chargingdevice LE in the form of a charging corotrone for charging theintermediate carrier 10; a character generator ZG with an LED comb forcharacter-dependent exposure of the intermediate carrier 10; developerstations EY, EM, EC and EB for inking in the charge images, which areproduced with the aid of the character generator ZG and discharged in acharacter-dependent fashion, on the intermediate carrier 10 with coloredtoner. The developer station EY contains yellow toner, the developerstation EM contains toner of the color magenta, the developer station ECcontains toner of the color cyan and the developer station EB containsblack toner. In order to remove the residual toner after development andtransfer printing, a cleaning station RS is provided with cleaning brushintegrated therein with associated suction device and a discharge device(not illustrated here). The developer stations EY, EM, EC and EB aredesigned to be replaceable and can be pulled out of, and pushed into theprinter or copier, for example by means of sliding guides. They aredesigned in the customary fashion and contain developer rollers forinking in the charge image. They can be driven individually and can beoperated or activated together or individually,

A transfer ribbon 12 is coupled to the intermediate carrier 10 by meansof a transfer station 11. The transfer ribbon 12 can be constructed as athermoadhesive transfer ribbon with a temperature-resistant carrierfabric, for example made of glass fiber fabric or temperature-resistantplastic, with an elastic cover layer of silicone or silicone-likematerial, for example rubber, arranged thereon. The transfer ribbon 12is also driven by electric motor and is guided by means of deflectionrollers 13, 14, 16 and 17. The deflection roller 13 is a component of atransfer printing and fusing station 18. It has a relatively largediameter and can be designed so as to be of heatable design in the formof a deflection roller. For this purpose, the deflection roller cancontain a heater in the form of a radiator. The deflection rollers 16and 17 are components of the transfer station 11 which, in the caseillustrated, contains a transfer corotrone 19. However, it is alsopossible to arrange, instead of an electrostatic transfer station ofthis kind, a mechanical transfer station in which, by means of contactbetween the transfer ribbon 12 and intermediate carrier 10, the tonerimages which are developed on the intermediate carrier 10 aretransferred to the transfer ribbon 12. Furthermore, the transfer ribbonis also assigned a heating station 20 with infrared heat source arrangedtherein and, if required, a cleaning device 15, 21 for the transferribbon, e.g. in the form of cleaning rollers.

Arranged in the region of the transfer printing and fusing station 18,parallel to the deflection roller 13, is a transfer printing and fusingelement 22 in the form of a heated transfer printing roller. It isguided on both sides and is supported by means of an elastic suspensionon the deflection roller 13 and thus on the transfer ribbon 12. It canalso be driven by electric motor. The region between the deflectedtransfer ribbon 12 or the deflection roller 13 and the transfer printingroller 22 is designated here as a transfer printing and fusing gap 23.The design of the transfer printing roller 22 is for example thatillustrated in FIG. 2. It consists of a metallic hollow roller 24 madeof aluminum with an elastic layer arranged thereon, for example made ofrubber 25 and an outer layer 26 made of fluoroplastics. Thefluoroplastics-containing outer layer can be for example of a thickness200 to 500 μm, "Teflon" being possible for use as afluoroplastics-containing material. Teflon refers here to a trade nameof Du Pont. Fluoroplastics-containing materials are for examplematerials made of tetrafluoroethylene, photopolymers oftetrafluoroethylene and hexafluoropropylenes and similar materials. Thehollow roller 24 can be of a thickness of 2 to 5 mm, the rubber layer 25can for example be of a thickness of 200 to 500 μm. However, otherdimensions are also possible, such as are described for example inEP-B1-0 186 314. Arranged in the hollow roller 24 is a heating device 27in the form of a heating radiator. It is also possible to heat thehollow roller 24 from the outside.

A cleaning device 28, e.g. in the form of a moving nonwoven belt or inthe form of brushes can be arranged for the purpose of cleaning thetransfer printing roller 22. The cleaning device 28 can be pivoted ontoand away from the transfer printing roller 22 in the directions of thearrows illustrated in FIG. 2 with the aid of a pivoting-on andpivoting-away mechanism.

A paper channel 30 is provided for feeding a recording medium 29 in theform of a single sheet or several single sheets arranged one next to theother to the transfer printing and diffusing gap 23 and has recordingmedium conveying devices 31 and 32 which are assigned to the paperchannel and have for example paper conveying rollers 33 or conveyingbelts which engage on both sides of the paper channel 30. Theserecording medium conveying devices convey the single sheets 29 from asupply area 34 to the transfer printing and fusing gap 23 and from thereonwards to a stacking device 35. A pre-heating device 36 for therecording medium can be assigned to the recording medium conveyingdevice 31 which is mounted upstream of the transfer printing and fusingstation 18 in the direction of conveyance of the recording medium. Thispre-heating device 36 can be designed to correspond to the heatingstation 20 and it can have radiator elements arranged on each side ofthe paper conveying channel 30. Instead of separate radiators, it isalso possible to heat e.g. the paper conveying rollers 33 of therecording medium conveying device 31.

The function of the arrangement will now be described below withreference to different operating modes. Here, the recording medium 29 tobe printed is fed in the form of a single sheet to the transfer printingand fusing station 18 in such a way that its back is directed upwardsand its front is directed downwards. In this way, the recording medium29 is stacked face down in the stacking device 35. However, the terms"front" and "back" are to be understood in a relative fashion in orderto describe the two opposite surfaces of the recording medium.

In order to reduce the expenditure in terms of control and in order toachieve a high accuracy of fit, the present printer or copier has aformat-independent printing output. This means that within a specifictime, a specific number of single sheets can be printed irrespective ofthe size of the formats, whether A4 or A5 or US formats. Thus, theprinting output is orientated with respect to the processing speed ofthe largest possible format. The single sheets 29 of different formatare thus fed to the transfer printing and fusing station 18 with astrictly prescribed timing code in strictly prescribed timing windowsand printed within these fixed timing windows irrespective of theirformat size.

For this purpose, image areas 38, within which charge images 37/1, 37/2can be produced at any desired point by means of the character generatorZG by exposing the photoconductor drum 10, are defined on thephotoconductor 10, clocked by the control of the printer or copier. Inthis way, the largest possible charge image which can be produced isalso determined by the image areas. The image areas 38 of constant sizebecome formed into continuous rows under their constant lengthdesignated by consecutive spacing. The consecutive spacing must bedimensioned such that it is greater than the largest possible recordingmedium format to be processed. The size of the image areas, and thus ofthe consecutive spacing, is determined such that the customary DIN andUS formats produce a maximum printing output and thus the predeterminedimage areas, and therefore the largest charge image which can beproduced, is utilized to a maximum degree.

By means of this measure, the single sheets of different formats can becontinuously fed to the printer or copier in a rigid time sequencepredetermined by the geometry and printed. This reduces the expenditurein terms of control considerably. In this process, the single sheets canbe fed by their front edges so as to be rigidly geometricallysynchronized with the start of the image areas 38, that is to say thesingle sheets are fed to the transfer printing and fusing station 18 bytheir front edge and printed in accordance with the fixed timingsequence of the edges of the image areas. In order to achieve thissynchronization and timing sequence, the circumferential length of thetransfer printing and fusing element and thus of the transfer printingroller is matched to the required length of the image areas 38 and thusto the strictly prescribed consecutive spacing.

Single-color duplex printing operating mode

In the single-color duplex printing operating mode, the latent characterimages on the back 37/1 and the front 37/2 of a sequence of singlesheets 29 to be printed are produced one after another by exposure inthe image areas 38 of the photoconductor 10, specifically, first theback 37/1 followed by the front 37/2, etc. The latent character imagesare then inked in with toner by one of the developer stations EB to EYas a function of the desired color and toner images 39/1 and 39/2 arethus produced. The toner images 39/1 and 39/2 are then electrostaticallytransferred to the transfer station 11 on the transfer ribbon 12. Thetransfer ribbon 12 is in a hot state. It is kept at this temperature bythe heating device 20. In this way, firstly back information and thenfront information is transferred to the transfer ribbon 12. As a resultof the effect of the heating device 27, the toner images change theirstate, they become pasty. The transfer ribbon 12 conveys the tonerimages to the back 39/1 and to the front 39/2 which follow one anotherdirectly in the transfer printing and fusing gap 23. The outer layer 26of the transfer printing roller 22 which consists of fluoroplasticslifts off the toner image of the back 39/1 from the transfer ribbon 12.It now adheres to the outer face of the transfer printing roller 22.Since the circumferential length of the transfer printing roller 22corresponds to the consecutive spacing and thus to the length of theimage areas 38, the start of the back toner image 39/1 reaches thefusing gap 23 again after one rotation of the transfer printing roller22. At this time, the start of the front toner image 39/2 is also in thesame position in the fusing gap 23, as is the front edge of therecording medium 29 to be printed. In accordance with the illustrationin FIG. 2, the transfer printing roller 22 and the transfer ribbon 12with the toner images 39/1 of the back and of the front 39/2 arranged onthem roll on the single sheet 29 and simultaneously print both sides ofit. In order to promote fusing, the recording medium can be pre-heatedby means of the heating device 36 (pre-heating device) before it is fedto the transfer printing and fusing station 18. The warm single sheetcoincides with the pasty toner image of the back 39/1 and the pastytoner image of the front 39/2. The print information can thus be fusedimmediately with the transfer onto the recording medium at lowinfluencing temperatures.

In the described duplex mode, operations occur with a timing sequencewith which a single sheet is fed after each second toner image. Thesingle sheets are guided in a straight fashion in the paper conveyingchannel 30 and the conveying speed is continuous. As a result of therigid geometrically exactly determined sequence, a high degree ofaccuracy of fit is achieved. Recording media are printed in anon-damaging fashion since the temperatures are low and in duplex modeit is only necessary to pass through the transfer printing and fusingstation 18 once.

Single-color simplex mode operation

In the single-color simplex mode operation, the corresponding chargeimages are produced one behind the other in the image areas 38, inked inin the developer station E according to the desired color, transferredto the transfer ribbon 12 and, in the illustrated case, transferred ontothe fronts of the single sheets fed one behind the other.

As a result of the continuous feeding of the single sheets, no undesiredtransfer of toner images onto the transfer printing roller 22 assignedto the back takes place.

As a result of the selected material combination of the outer face ofthe transfer printing roller 22 and the outer face of the transferribbon 12, the toner images are normally transferred completely to thesingle sheets 29 without residues of the toner remaining on the transferribbon 12 or the transfer printing roller 22. Faults occurring in theelectrophotographic process can, however, lead to a build up of toner atfault points which may on occasion lead to residues of toner remainingon the transfer printing roller or the transfer ribbon 12. In order toremove these toner residues, a cleaning device 21 in the form of one ormore cleaning rollers 15, 21 can be assigned to the transfer ribbon 12and a cleaning device 28 for example in the form of a nonwoven cleaningstation which can be pivoted on and away, can be assigned to thetransfer printing roller 22. The pivoting on and away of the nonwovencleaning station 28 takes place here under the control of the printer orcopier control system as a function of the toner image sequence.Cleaning of the transfer printing roller 22 can then take place withpivoted-on nonwoven cleaning station 28, for example when there is notoner image to be printed on the transfer printing roller 22 or forexample during the transfer printing onto the single sheet. Byappropriately controlling the sequence of toner images in conjunctionwith the feeding of the single sheets, cleaning cycles can thus beincluded within the scope of the printing timing sequence.

Color print mode operation

With the described arrangement, color printing of single sheets is alsopossible, specifically with a multi-color image on the back and asingle-color image on the front or with multi-color images on the backwithout printing the front.

For this purpose, a sequence of latent character images, associated withpartial color images, for the back and a latent character image for thefront are produced in the images areas 38 by means of the charactergenerator ZG. These latent character images are then inked in by meansof the developer stations EB to EY and the toner images produced in thisway are transferred to the transfer ribbon 12. In order to print theback in color, the heated, pasty partial color toner images are thentaken up by the transfer printing roller 22 in a superimposing fashionand simultaneously transferred together with a single-color toner imagefor the front which also adjoins the transfer ribbon 12 to a fed-insingle sheet in one operation.

By omitting the toner image for the front, the fed-in single sheets 29can be color printed in sequence on their back.

In order to print the recording media 29 in color, it is not necessaryto change the fusing station 18 and the paper guidance. The selection ofcolor and of the operation modes is made simply by appropriatelyactuating the character generator ZG, and the developer stations EB toEY.

As a result of the long residence time of the toner images firstly onthe transfer ribbon 12 and subsequently on the heated transfer printingroller 22, the fusability of the color toner which is difficult to fuseis improved.

By appropriately actuating the character generator in conjunction with aselective activation of the developer stations EB to EY, mixed operationwith different modes of operation is also possible.

Although the present invention has been described with reference to aspecific embodiment, those of skill in the art will recognize thatchanges may be made thereto without departing from the scope and spiritof the invention as set forth in the appended claims.

    ______________________________________                                        List of reference symbols                                                     ______________________________________                                        10        Intermediate carrier, photoconductor drum                           LE        Charging device                                                     ZG        Character generator                                                 EY        Developer station, yellow                                           EM        Developer station, magenta                                          EC        Developer station, cyan                                             EB        Developer station, black                                            RS        Cleaning station                                                    11        Transfer station                                                    12        Transfer ribbon                                                     13        Deflection roller (heated)                                          14        Deflection roller                                                   15        Cleaning roller                                                     16        Deflection roller of the transfer station                           17        Deflection roller of the transfer station                           18        Transfer printing and fusing station                                19        Transfer corotrone                                                  20        Beating station, heating device                                     21        Cleaning device, cleaning roller                                    22        Transfer printing and fusing element,                                         transfer printing roller                                            23        Transfer printing and fusing gap                                    24        Hollow roller                                                       25        Rubber layer                                                        26        Outer layer                                                         27        Beating device, radiator                                            28        Cleaning device, nonwoven cleaning                                  29        Recording medium                                                    30        Paper conveying channel                                             31/32     Recording medium conveying devices                                  33        Paper conveying rollers                                             34        Supply area                                                         35        Stacking device                                                     36        Preheating device                                                   37/1      Charge image (back)                                                 37/2      Charge image (front)                                                38        Image areas                                                         39/1      Toner image (back)                                                  39/2      Toner image (front)                                                 ______________________________________                                    

I claim:
 1. An apparatus for printing the front and back of a recordingmedium in a reproducing device operating according to a transferprinting principle, comprising:an electrographic device having aphotoconductor for producing a sequence of toner images on thephotoconductor; a transfer printing and fusing station having a transferprinting and fusing gap; a transfer ribbon having electrostatic transfermeans for receiving the toner images from the photoconductor and forconveying the toner images to said transfer printing and fusing station;a heating device for heating the toner images in such a way that theyare in a pasty, sticky state; said transfer printing and fusing gaphaving said transfer ribbon arranged on one side and a transfer printingand fusing element arranged on an opposite side in such a way that thetransfer ribbon and the transfer printing and fusing element aresupported elastically on one another, the transfer printing and fusingelement and the transfer ribbon having surfaces which receive the tonerimages of such a quality that on contact with the transfer ribbon, thetransfer printing and fusing element removes a toner image which isarranged on the transfer ribbon; and a recording medium conveying meansfor feeding the recording medium to the transfer printing and fusing gapsuch that, as the recording medium passes through the gap, the transferprinting and fusing element and the transfer ribbon roll on therecording medium and, the toner images are transferred to the recordingmedium.
 2. The apparatus according to claim 1, wherein said transferprinting and fusing element is constructed as a heated roller.
 3. Theapparatus according to claim 2, wherein said transfer printing andfusing element has a circumferential length which is sized in accordancewith a strictly prescribed consecutive spacing of image areas whichreceive the toner images on the photoconductor.
 4. The apparatusaccording to claim 3 further comprising a heating device which heats thetransfer ribbon.
 5. The apparatus according to claim 1, wherein saidtransfer printing and fusing element is constructed as a heated ribbon.6. The apparatus according to claim 5, wherein said transfer printingand fusing element has a circumferential length which is sized inaccordance with a strictly prescribed consecutive spacing of image areaswhich receive the toner images on the photoconductor.
 7. The apparatusaccording to claim 6 further comprising a heating device which heats thetransfer ribbon.
 8. The apparatus according to claim 1, wherein saidtransfer printing and fusing element has a circumferential length whichis sized in accordance with a strictly prescribed consecutive spacing ofimage areas which receive the toner images on the photoconductor.
 9. Theapparatus according to claim 8 further comprising a pre-heating meansfor pre-heating the recording medium before it is fed to the fusing gap.10. The apparatus according to claim 8 further comprising a heatingdevice which heats the transfer ribbon,
 11. The apparatus according toclaim 10 further comprising a pre-heating means for pre-heating therecording medium before it is fed to the fusing gap.
 12. The apparatusaccording to claim 1 further comprising a cleaning device assigned tothe transfer printing and fusing element and activatable as required.13. The apparatus according to claim 12 further comprising a heatingdevice which heats the transfer ribbon.
 14. The apparatus according toclaim 12 further comprising a pre-heating means for pre-heating therecording medium before it is fed to the fusing gap.
 15. The apparatusaccording to claim 1 further comprising a heating device which heats thetransfer ribbon.
 16. The apparatus according to claim 15 furthercomprising a pre-heating means for pre-heating the recording mediumbefore it is fed to the fusing gap.
 17. The apparatus according to claim1 further comprising a pre-heating means for pre-heating the recordingmedium before it is fed to the fusing gap.
 18. The apparatus accordingto claim 1, wherein a surface layer of the transfer ribbon comprises asilicon material; and a surface layer of the transfer printing andfusing element comprises a fluoroplastic material.
 19. A method forsimultaneously printing the front and back of a recording medium in areproduction device which operates according to a transfer printingprinciple, comprising the following steps:producing a sequence of tonerimages by means of an electrophotographic process on a photoconductor, afirst toner image of the sequence being for a back of a recording mediumand a second toner image being for a front of the recording medium;electrostatically transferring the sequence of toner images to atransfer ribbon; feeding the sequence of toner images on the transferribbon to a transfer printing and fusing station with a transferprinting and fusing gap for receiving the recording medium, on one sideof the gap the transfer ribbon is arranged and on the other side of thegap a transfer printing and fusing element is arranged; heating thetoner images to a temperature near to a fusing temperature of the tonermaterial; transferring the first toner image to the transfer printingand fusing element; feeding a recording medium to the transfer printingand fusing gap, the transfer printing and fusing element with the firsttoner image and the transfer ribbon with the second toner image rollingon the recording medium in order to print simultaneously the front andback of the recording medium and to fuse the toner images on therecording medium.
 20. The method according to claim 19, wherein the stepof producing a sequence of toner images is further defined in that tonerimages are produced on the photoconductor in image areas which arearranged in a strictly prescribed consecutive spacing, and in that thestep of feeding the sequence of toner images is further defined in thatthe circumferential length of transfer printing and fusing element isselected in accordance with this consecutive spacing.